The present invention relates generally to current and voltage sensing devices for electrical systems, and more particularly to automatically resetable combined alternating current fault and voltage indicators.
With the increased use of underground electrical distribution systems wherein primary and secondary feeder cables are directly buried in the ground, the need has arisen for improved detection apparatus for determining the location of a short circuit or fault in the system cables or associated electrical components, and the voltage level present in a particular circuit of the system.
Various types of fault indicators have been constructed for detecting faults in such systems, including clamp-on type fault indicators, which clamp directly over cables in the system, and test-point type fault indicators, which are mounted over test points in the cables or associated connectors. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicator be physically reset following each fault, or of the automatically reset type, wherein a fault indication is reset upon restoration of line current. The automatically reset type is beter adapted for use in underground distribution systems in that it is not necessary to gain access to the fault indicator following occurrence of a fault. Examples of such automatically reset fault indicators are found in products manufactured by E. O. Schweitzer Mfg. Co. of Mundelein, Illinois, in U.S. Pat. Nos. 3,676,740, 3,906,477 and 4,063,171 of the present inventor, and in the copending application of the present inventor, Ser. No. 958,103, filed Nov. 6, 1978.
Detection of fault currents by self-resetting fault indicators is often most advantageously accomplished by means of a read switch located within the indicator housing having contacts in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the contacts close and actuate circuitry which magnetizes an internal pole piece to position to a trip position a target indicator visible from the exterior of the indicator. Upon restoration of current in the conductor another circuit is actuated to reposition the target indicator to a reset non-fault indicating position. Preferably, as in the afore-identified application Ser. No. 958,103, power for the trip and reset circuits is derived from the circuit being monitored, by capacitive coupling, to preclude the need for a separate power source for the fault detector.
In many applications the need arises for a voltage indication in addition to a fault indication so that the presence of voltage, and the level of voltage in the monitored circuit, can be readily determined. Heretofore this has been accomplished by a separate device, typically employing a circuit of the capacitor-discharge type, which provides a flashing rate proportioned to circuit voltage level. One preferred form of such a voltage indicator for use on a test point terminal is described in the copending application of the present inventor, Ser. No. 895,151, filed Apr. 10, 1978, now U.S. Pat. No. 4,152,643.
The present application is directed to a combined indicator wherein both fault and voltage indications are simultaneously provided in a single compact device with a minimum number of components, thereby providing maximum convenience of use and economy of manufacture.
Accordingly, it is a general object of the present invention to provide a new and improved combined fault and voltage indicator.
It is a more specific object of the present invention to provide a compact and economical combined fault and voltage indicator which provides simultaneous indications of fault occurrence and operating voltage.